How to control broad mites in greenhouses and sheds? Understanding the occurrence pattern is key

In greenhouse fruit and vegetable production, curled and shrunken growing points of plants, deformed and cracked fruits are often seen, causing serious losses to production. Because the temperature and humidity inside the greenhouse are very suitable for the growth and reproduction of broad mites, and fruit vegetables are their main targets, and the mites are extremely small and invisible to people, timely control is impossible. Therefore, in recent years, the area of occurrence and damage has been growing larger and larger, which should attract great attention from producers.

Broad mites belong to the class Arachnida, order Acariformes, family Tarsonemidae, and are harmful microscopic pests. They mainly damage cucumbers, eggplants, tomatoes, green peppers, and green beans among fruit vegetables in greenhouses. The mites gather on the young and tender parts of vegetable plants and cause damage by piercing and sucking. The back of damaged leaves appears grayish-brown or yellowish-brown with an oily luster (this is the main difference from viral diseases), and the leaf edges droop and curl. Damaged leaves at the heart of the plant become narrow, stiff and upright, wrinkled, twisted, and deformed; in severe cases, the top dries up and dies. Damaged flowers do not open and fall off. The skin of damaged fruits becomes rough and suberized, turning yellowish-brown and lusterless. Damaged eggplant and tomato fruits crack, resembling a split steamed bun, taste bitter and astringent, and are inedible.

Because the mites are extremely small and invisible to the naked eye, the oval-shaped transparent bodies can only be observed under a dissecting microscope, so the above damage symptoms are very easily mistaken for physiological diseases or viral diseases.

Adult broad mites overwinter in winter on vegetable plants, at the roots of weeds, or in soil cracks inside greenhouses, and begin to reproduce and cause damage in March to April of the following spring. The suitable temperature for development and reproduction is 16 to 23 degrees. At a relative humidity of 80% to 90%, one generation can be completed in 7 to 10 days. Mature male mites are active; when the feeding site becomes old, they can carry female nymph mites to transfer to tender tip areas, mate, reproduce, and continue to cause damage.

Because broad mites have a short life cycle, extremely strong reproductive capacity, damage many crops and are hidden, and because they are acarid pests, general insecticidal drugs have unsatisfactory control effects, control is relatively difficult. Therefore, comprehensive prevention must be taken as the main approach, and only comprehensive control can achieve good results.

1. Use sulfur powder fumigation to eliminate the source of mites. Although broad mites can also survive in greenhouses in winter, their population is small, reproduction is slow, and resistance is low. This favorable opportunity should be seized to thoroughly eradicate them in time to prevent spread. The method is: after pulling up the vines of the previous crop in the greenhouse and before raising seedlings for the next crop, carefully remove residual branches and fallen leaves, pull out weeds, seal the greenhouse well, mix 0.5 kg of sulfur powder with an equal amount of dry sawdust per 100 sq m of greenhouse, divide it into 2 to 3 piles and light them on a windless night (preferably on a rainy or snowy day), fumigate for 24 hours, then open up for ventilation. After 5 to 7 days, seedlings can be raised or vegetable seedlings can be planted. But it must be noted that when using sulfur powder fumigation, growing vegetables and people or livestock must be strictly prohibited inside the greenhouse to prevent accidents. In addition, this method must not be used on vegetables during the growing period. (This method also has very good effects on controlling black spot disease, late blight, and other pests.)

2. Crop rotation. Rotating fruit vegetables with cold-tolerant leafy vegetables such as chives, lettuce, pak choi, rapeseed, and cilantro can reduce damage.

3. Chemical control. Chemical control of broad mites should adhere to the principle of early treatment and thorough treatment. When a small number of damaged plants are found, the damaged plants can be pulled up and burned in time, and at the same time, spray alternately with 3000 to 4000 times dilution of Miechongling and 2000 times dilution of 5% nisolan emulsifiable concentrate every 6 to 7 days; they must not be mixed. Spray 3 to 5 times consecutively. Combined with fumigation using insecticidal smoke agents, once every 5 to 7 days, fumigating 2 to 3 times consecutively, the effect is better.

Production practice has proven that pesticides commonly used in the past, such as dicofol, dichlorvos emulsifiable concentrate, and dimethoate, have clearly caused broad mites to develop resistance due to long-term use, so their control effects are poor or basically ineffective. They should be avoided to prevent delaying the timing of control.